Bearing assembly for a drill bit

ABSTRACT

The cutter joint is formed on a trunnion by a peripheral radial-trust rolling bearing whose internal ring ( 4 ) together with rolling bodies ( 6 ) and a cage ( 7 ) are arranged on the trunnion ( 2 ) and locked thereon by snap ring ( 15 ), an external bearing ring ( 5 ) is inserted into the cutter ( 3 ) and locked therein by a circlip ( 12 ). The end radial-trust rolling bearing comprises an external ring ( 9 ) inserted into the cutter and internal ring ( 8 ) which is arranged on the trunnion together with rolling bodies ( 10 ) and cage ( 11 ) in such a way that it is slidable and trusted to the trunnion through a spring ( 16 ). In one embodiment, the inventive bearing assembly comprises a trust needle bearing arranged between the cutter and the trunnion through an axial spring. Said invention makes it possible to remove sliding friction between the adjacent rolling bodies in bearings, reduce heat generation in a bearing chamber, limit the deviation of rollers in conical bearings from a linear contact with bearing races, automatically remove bearing plays, thereby excluding heat blocking during a bit operation. The invention also simplifies the process of production of the drill bit, makes it possible to carry out non-destructive tearing of the cutter and to reuse the arm thereof. The technical result of the invention increases the service life of the bearing assembly, increases load applied to the drilling bit and rotating velocity thereof, thereby increasing drilling speed and drilling rate for a bit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is an U.S. national phase application under 35 U.S.C. §371 based upon co-pending International Application No. PCT/UA2004/000042 filed Jun. 29, 2004. Additionally, this U.S. national phase application claims the benefit of priority of co-pending International Application No. PCT/UA2004/000042 filed Jun. 29, 2004, and Ukrainian Application No. UA 2003098141 filed Sep. 1, 2003. The entire disclosures of the prior applications are incorporated herein by reference. The international application was published Mar. 10, 2005 under Publication No. WO 2005/021923 A1.

FIELD OF TECHNOLOGY

The invention belongs to roller cutter drill bits for drilling boreholes, more specifically to the design of bearing supports, and also to the design of bits with demountable components.

PRIOR STATE-OF-THE-ART

It is well known that there exist bearing supports for roller cutter drill bits having roller cutters mounted on foot trunnions by means of rolling bearings, as radial ones cylindrical roller bearings—peripheral (nearest to the trunnion base) and end (located on the trunnion end) bearings being used, and as a radial-thrust lock bearing (excluding spontaneous removal of a roller cutter from a trunnion, and also forming a rest relative to axial loads on the roller cutter, the axial loads acting in the direction from the trunnion end to the base thereof) a ball bearing is used, the bearings having no cages, and their bearing races, and their bearing races are made in the trunnion and roller cutter bodies (see, e.g., Maslennikov I. K. Drilling tools. Reference book.—Moscow, Nedra pub., pgs. 34-36).

The basic disadvantages of the design of such supports are as follows:

-   a) The impossibility of mounting cages inside the bearings (rolling     bodies are inserted separately into bearing races in the process of     support assembly), as a result of which, first, it is impossible to     orientate the rotation axes of rollers relative to bearing races in     a way, sufficiently strict and independent from radial play in     bearings, second, contact is possible between roller faces and side     surfaces of bearing races with the appearance of rotational forces     of a roller longitudinal axis and a corresponding deviation of the     axis from a design location, third, the adjacent rolling bodies, on     account of their opposing movement direction at the contact between     them, undergo sliding friction and mutually wear out by abrasion. -   b) The possibility of jamming rolling bodies between the trunnion     and the roller cutter as a result of a higher thermal expansion of     the trunnion relative to a thermal expansion of the roller cutter in     the process of bit operation (on account of a more intensive cooling     of the roller cutter rotating in the drilling mud). To avoid such     jamming, it is necessary to provide radial play between the rolling     bodies and the bearing races of the bearings, i.e. to provide     initial play in the support, which excludes the possibility of     making assembly interference fit in bearings, increases the     possibility of the above-mentioned rotation of roller axes,     decreases the load capacity and service life of bearings. -   c) The impossibility of automatically regulating the play (providing     an interference fit in bearings) in the process of bit operation.

The indicated disadvantages result in a transformation of roller contacts with bearing races from linear to point type—with a sharp growth of contact pressure levels, an intensive wear of supporting surfaces, steadily increasing play values, loss of a design geometrical shape of rolling bodies, overheating of a bearing support, which ultimately brings to a failure of a bearing support and, therefore, of the bit as a whole (in the majority of cases, the serviceability of roller cutter arrangements being still maintained). Besides, the indicated rotation of roller axes and the loss of their linear contact with bearing races results in a decrease of the bearing load capacity, so that in practice it is necessary to limit axial loads on bit, thus limiting drilling efficiency.

Among disadvantages of similar bearing assemblies for drill bits, wear can also be noted practically in all components and bodies, with an impossibility of their repeated use, technological complexity of manufacturing the internal surface of the roller cutter (boring, then thermochemical treatment, further internal grinding) and complexity of making a toroidal raceway of the lock-type ball bearing inside the trunnion in a sufficiently precise manner.

The known substantial attributes of the represented analogue of a bearing support relative to the offered invention comprise at least one foot with a trunnion, a roller cutter, and rolling bearings.

A known modification of the indicated analogue comprises a bearing assembly for a drill bit, inclusive a peripheral cylindrical roller bearing, and a lock ball bearing, in which instead of an end cylindrical roller bearing a radial plain bearing is utilized (see the above-mentioned book, pgs. 35-36). This modification is characterized by the same disadvantages as the foregoing analogue. Moreover, the use of plain bearings means an increase in heat release in the support, due to the fact that a sliding friction factor substantially exceeds a rolling friction factor.

The known substantial attributes of this analogue, relative to the offered invention, are presented with at least one foot having a trunnion, a roller cutter, and a radial-thrust lock rolling bearing.

Another modification of the first of the above-mentioned analogues is a drill-bit bearing support which, in addition to the lock ball bearing, is provided with a thrust-roller rolling bearing with a cage (see, e.g., Great Britain Patent 2 380 500 A, Int. Cl.7 E21B 10/22). This bearing support modification is characterized by the same disadvantages as it is the case with the first analogue, because the rest of bearings—peripheral, lock ball-type and end ones—have no cages. Also, the requirement to harden and grind the bearing races of the thrust bearing, the said processes being performed directly on the opposite surfaces of the trunnion and the roller cutter, belong to disadvantages of this analogue. The known substantial attributes of this analogue relative to the offered invention are presented with at least one foot having a trunnion, a roller cutter, and rolling bearings, inclusive a thrust bearing with a cage.

Also, a drill bit is known with a rolling support, the lock of which is formed conventionally with a ball bearing, and the peripheral and end bearings are made in the form of radial-thrust conical bearings—without cages, with bearing races in the trunnion and roller cutter bodies,—moreover, the geometrical axes of rollers, of both the peripheral bearing and the end bearing, intersecting the geometrical axis of the trunnion on the side opposite to its base (see, e.g., USSR inventor's certficate 1229297 A1, Int.Cl.4 E21B 10/22). This analogue is characterized by the same disadvantages as it is the case with the first of above-mentioned analogues. The said orientation of conical roller axes permits of reacting to no two-side axial loads on the roller cutter, and requires the use of a ball lock-type bearing. Besides, to make two pairs of interconnected conical bearing races, with a sufficient precision, on the trunnion and inside the roller cutter, in the conditions of bit production process, is rather a complicated technological problem.

The known substantial attributes of this analogue relative to the offered invention are presented with at least one foot having a trunnion, a roller cutter, a lock radial-thrust roller bearing (ball-type), a peripheral radial-thrust rolling bearing, and an end radial-thrust rolling bearing.

Taking into account the technical essence, the achieved technological effect and the set of substantial attributes of an analogue, which is nearest to the offered arrangement, are presented by a bearing assembly for a drill bit, comprising at least one foot with a trunnion, a roller cutter, a lock radial-thrust conical rolling bearing, set into the axial rest between the roller cutter and the trunnion, an end radial plain bearing, and a thrust plain bearing between the trunnion end and the roller cutter, the external and internal bearing races of the lock bearing being made in the roller cutter and trunnion bodies, respectively, the geometrical axes of this bearing rollers intersect on the side, opposite to the trunnion base, and the face surfaces of the rollers directly contact the trunnion with their one side, and on the opposite side—with an intermediate sleeve, inserted into and united with the roller cutter on the side of the trunnion base (see, e.g., USA patent 4 172 502; Int.Cl.2 E21B 9/10; E21C 13/02, Holland priority as of Aug. 23, 1976)—prototype.

Note. In the prototype description there is an assertion that the peripheral lock bearing is equipped with a cage. However, this assertion is unsubstantiated, because the mounting of a cage, terminating the installation of rollers on a separate internal ring of an ordinary bearing, is a complex technological process, and practically unrealizable as applied to the mounting of a cage on the drill bit trunnion, which is evidenced by all the world practice of the production of drill bits, the bearing supports of which have no cages, except for a thrust roller bearing inserted into the support as a set of rollers with a cage, where the design of the support allows for it (see the above-mentioned Great Britain patent). In connection to this, the presence of cage among the above substantial attributes of the prototype is not taken into account by the applicants. On account of this, obviously, the attribute of the presence of a cage is not indicated by the inventor in the claims to the invention-prototype.

To the prototype disadvantages belong:

-   the axes orientation of conical rollers of the lock bearing with the     intersection of these axes on the side opposite to the trunnion     base, which excludes the possibility of axial load transmission from     the side of a drilled borehole wall to the trunnion through the     conical surfaces of the bearing, and leads to the transmission of     such a load through the opposite faces of the rollers—with an     appropriate sliding friction, abrasion of contacting surfaces,     additional heat release in the bearing cavity, appearance of the     moment of roller rotation relative to the bearing races,     transformation of the contact between the rollers and the bearing     races from a linear to a point type, abrupt increase in contact     pressures, and an extensive wear of the bearing; -   the impossibility of an automatic regulation of play (regulation of     interference fit values) in the bearing support in the bit operation     (with the consequences considered above); -   the possibility of jamming a bearing support as a result of the     trunnion overheating relative to the roller cutter; -   the relative limitation of the bearing base in connection with a     series arrangement of the bearing and the component, inserted into     and connected with the roller cutter on the side of the trunnion     base, due to which the load capacity of a bearing support decreases,     i.e. there is a decrease in one of the principal     operational_indicators of drilling efficiency; -   the impossibility of a repeated use for the foot due to the     execution of the roller bearing bearing races directly in the     trunnion, to the wear and loss of design dimensions of bearing races     on the trunnion in the process of bit machining; -   the complexity of making conical bearing races in the roller cutter     and trunnion bodies, indicated above.

The known substantial attributes of the prototype relative to the offered invention are presented by at least one foot with a trunnion, a roller cutter, a_radial-thrust rolling bearing, locking the roller cutter on the trunnion by means of a spread piece in the axial gap between the trunnion and the component, inserted into and fixed in the roller cutter on the side of the trunnion base, and an end bearing.

Disclosure of the Invention

As the basis for the invention, the tasks are set of:

-   increasing the load capacity of a bearing support; -   increasing the service life of a bearing support; -   decreasing the sliding friction share in a bearing support with an     appropriate decrease in heat release and wear of contacting     surfaces; -   automatically regulating the interference fit of bearings in drill     bit operation; -   excluding the thermal jamming of a support; -   simplifying the technology of executing the internal surface of a     roller cutter; -   simplifying the technology of foot manufacture; -   providing the possibility of a repeated use for a foot and other     components of the bearing support.

The known substantial attributes of the offered bearing assembly for a drill bit are presented by at least one foot with a trunnion, a roller cutter, a radial-thrust rolling bearing, locking the roller cutter on the trunnion by means of a spread piece in the axial gap between the trunnion and the component, inserted into and fixed in the roller cutter on the side of the trunnion base, and an end bearing.

An independent substantial distinctive attribute of the invention consists in the fact that the radial-hrust rolling bearing, locking the roller cutter on the trunnion, is executed in the form of a separate internal ring and a separate external ring with bearing races, and rolling bodies, corresponding to them. The dependent substantial distinctive attributes of the invention are:

-   -   the provision of the radial-thrust rolling bearing, locking the         roller cutter on the trunnion, and executed in the form of a         separate internal and a separate external ring, with a cage;     -   the manufacture of an end bearing in the form of a separate         internal ring and a separate external ring with bearing races,         and cylindrical rollers;     -   the execution of the end bearing in the form of a radial-hrust         conical rolling bearing, comprising a separate internal ring and         a separate external ring with bearing races, and rolling bodies,         corresponding to them, united by a cage, the internal ring of         this bearing being fitted on the trunnion with the possibility         of free movement along the trunnion in combination with the         execution of an axial rest, limiting such movements, on the         trunnion, and of mounting a spring between this rest and the         bearing;     -   the provision of the bearing support with a thrust bearing,         executed in the form of a pair of supporting rings, between         which a cage with rolling bodies is located, moreover, this         bearing resting against the trunnion end through a spring, e. g.         a disk spring;     -   arrangement of the bearing, nearest to the trunnion base, inside         the component, inserted into and fixed in the roller cutter on         the side of the trunnion base, the indicated component being         screwed into the roller cutter on the side of the trunnion base         to the rest of the radial-thrust bearing against the trunnion;     -   execution of the component, inserted into and fixed to the         roller cutter on the side of the trunnion base, in the form of a         split spring ring.

The execution of the lock radial-thrust bearing in the form of a separate internal ring and a separate external ring with bearing races, and of appropriate rolling bodies, united by a cage, jointly with the execution of the end radial bearing and the thrust bearing in the form of a unified radial-thrust end bearing, consisting of a separate internal ring and a separate external ring with bearing races, and of appropriate rolling bodies, united by cages:

-   -   excludes the axial rest between the roller cutter and the         trunnion through the roller faces of the lock bearing (see         prototype);     -   provides a locking support of the roller cutter on the foot         trunnion over the rolling surfaces of the lock bearing, hence,         with a minimum friction factor;     -   owing to cages, excludes friction between adjacent rolling         bodies, decreasing heat generation in the bearing cavity, and         provides the stable orientation of roller axes, excluding their         non-linear (point) contact with bearing races, and corresponding         pitting destruction of bearing races and rollers themselves,         which results in increasing the load capacity and the service         life of a support;     -   provides the simplified technology of manufacturing the         supporting surfaces of the foot and the roller cutter (exclusion         of making complex toroidal surfaces, of performing         thermochemical and grinding operations);     -   owing to demountable execution of internal bearing rings and the         exclusion of a corresponding wear of the foot, provides the         possibility of their repeated use.

The execution of the end bearing in the form of an internal ring and an external ring with bearing races, and of corresponding cylindrical rollers, allows of increasing the radial load on the bearing support and its service life.

The fit of the internal ring of the end radial-thrust bearing with, a possibility of this ring sliding along the trunnion in combination with the axial rest of this ring against the trunnion through the spring, provides axial movements of this bearing in response to thermal deformations of the trunnion and the roller cutter, thus excluding the thermal jamming of the bearings and the failure of the support on the whole, and automatically provides the exclusion of play in the end radial-hrust bearing.

The execution of the thrust bearing in the form of a pair of supporting rings and a cage, with rolling bodies between them, allows of simplifying the technology of manufacturing the foot and the roller cutter, excluding the necessity to perform appropriate thermochemical treatment and grinding operations on the supporting surfaces of the trunnion and inside the roller cutter.

The arrangement of the thrust bearing to a rest between the roller cutter and the trunnion through a spring excludes play in this bearing, and in the lock radial-hrust bearing, under alternate axial loads on the roller cutter.

The location of the lock bearing inside the intermediate sleeve, screwed into the roller cutter on the side of the trunnion base, provides an increase of the bearing base (relative to the prototype) and, therefore, a decrease of reactions on the bearings under the effect of bending moments, acting on the roller cutter.

The rest of the roller cutter against the lock bearing directly through the split spring ring, inserted into the roller cutter on the side of the trunnion base, provides an increase of the bearing base, and also the possibility of a nondestructive disassembly of the roller cutter and, in combination with demountable internal bearing rings, the possibility of a repeated use of the foot and other components of the support that have retained their serviceability.

A SHORT DESCRIPTION OF DRAWINGS

Isolated examples of manufacturing a bearing assembly for a drill bit are illustrated in the drawings, according to the invention:

FIG. 1—a fragment of the foot with a bearing support and a roller cutter in a meridional section;

FIG. 2—the same in modifications of the design (the roller cutter is shown fragmentally here);

FIG. 3—the same in a modification with the conventional location of the lock bearing-between a peripheral bearing and an end bearing.

MODIFICATIONS OF THE INVENTION EXECUTIVE

In accordance with the substantial attributes of the invention, the bearing support comprises (see FIG. 1) at least one foot 1 with a trunnion 2, on which roller cutter 3 is arranged by means of a bearing support. The bearing support comprises a lock radial-thrust thrust rolling bearing, in this example—a roller conical one with internal ring 4, external ring 5, rollers 6 and cage 7, and an end radial-thrust roller bearing with internal ring 8, external ring 9, rollers 10 and cage 11. The locking of the roller cutter on the foot trunnion is formed by split spring ring 12, inserted into the roller cutter on the side of the trunnion base, and a lock radial-thrust bearing, external ring 5 of which rests through split ring 12 against the roller cutter, and internal ring 4 rests through split spring ring 15 with its front (supporting) face against the trunnion, so that the lock bearing resists axial loads acting on the roller cutter on the side of the trunnion base, excluding a possibility of the roller cutter random removal from the trunnion. According to this, in the present example of a conical radial-thrust bearing, geometrical axes 13 of rollers 6 intersect with geometrical axis 14 of trunnion 2 on the side, opposite to the trunnion end. The end radial-thrust conical bearing is arranged for resistance to opposite direction forces, in accordance with which geometrical axes 17 of its rollers 10 intersect with geometrical axis 14 of the trunnion on the side, opposite to the base of trunnion 2. The lock bearing and the end bearing also serve to transmit radial loads, acting on the roller cutter, to the trunnion. Internal ring 8 of the end bearing is mated with trunnion 2 with a possibility of free movement along the trunnion. In addition, bearing ring 8 rests against the trunnion through disk spring 16.

In another example of a bearing support modification (see FIG. 2), between roller cutter 18 and trunnion 19, an axial bearing, comprising a pair of supporting rings 21 and 22 with bearing races and cage 23 with rolling bodies, is arranged to a rest through disk spring 20. The end bearing, in this modification—a cylindrical bearing with internal ring 25, external ring 26 and rollers 27, transmits only radial loads from the roller cutter to the trunnion. The rest of roller cutter 18 against a lock radial-thrust bearing in this modification is effected through sleeve 24, which is screwed into the roller cutter to an interference fit of this bearing, moreover, the bearing being located inside the sleeve.

In the modification according to FIG. 3 the support is executed close to a bearing scheme, conventional for drill bits: lock radial-thrust ball bearing 28 is arranged between peripheral roller bearing 29 and end roller bearing 30. The locking of roller cutter 31 on trunnion 32 of foot 33 is formed by spring split ring 34, an external ring of bearing 29, lock bearing 28, and retaining split spring ring 35, inserted into trunnion 32.

Industrial Applicability

In drill bit operation with a bearing support according to the modification in FIG. 1 disk spring 16 in combination with a sliding fit of internal bearing ring 8 automatically provides interference fit (exclusion of play) in a conical end bearing under changing temperature conditions of the trunnion and the roller cutter (the latter cools intensively as it rotates in a drilling mud, unlike the trunnion), when the axial dimensions of the trunnion and the roller cutter change in a different way. A radial jamming of the bearing support is excluded due to the fact that the overheating of the trunnion and the internal bearing rings causes the movement of conical rollers in the direction of decreasing the interference fit of the bearing, i.e. transforming radial interference fit into an axial interference fit, which is compensated by the action of spring 16.

In the modification of fig.2 disk spring 20 automatically retains the interference fit (excludes play) in the lock bearing, when the direction and the amount of axial load on the roller cutter is changed, and excludes the thrust bearing jamming under conditions of a thermal elongation of the trunnion relative to the roller cutter. In the modification of FIG. 3 the axial spread of lock bearing 28 between the trunnion and the roller cutter is provided through bearing 29.

In all the examined design modifications, the rolling bearings provide a minimum, as compared to plain bearings, heat generation in the bearing support, which is also facilitated by cages, thus excluding sliding friction between adjacent rolling bodies. As a consequence, the decrease of temperature in the bearing cavity provides the operation of elastomer seals (thermosetting, as is known), pressurizing the cavity. On the other hand, a decrease in heat generation allows for increasing loads on the bit and the rotational speed, which means an increase in drilling efficiency.

As it happens, the use of bearings with internal and external rings, arranged separately from the roller cutter and the trunnion, after turning operation, excludes the necessity to perform thermochemical treatment and subsequent grinding of the corresponding surfaces of the roller cutter and the trunnion, thus simplifying, on the whole, the technology and labour input into the drill bit manufacture.

Owing to the fact that the trunnion, when the offered bearing support is in operation, is free from contact with rolling bodies and undergoes no wear, it is possible, after the arrangement is in a used condition, to provide nondestructive disassembly of the roller cutter, e.g. by means of screwing it together with sleeve 24, in the modification of FIG. 2, and repeated use of the foot and other components of the bit, which have retained their serviceability.

Technical Result

Technical results of the invention represent the possibility of increasing loads on drill bit, increasing rotational speed, enhancing service life of drill operation—with a corresponding increase in drilling efficiency (drilling speed and hours per bit), of simplifying the technology of manufacturing drill bits, and also a possibility of repeated use of the foot and other components. 

1-8. (canceled)
 9. A bearing assembly for a drill bit comprising: at least one foot with a trunnion; a roller cutter; a radial-thrust roller bearing, locking said roller cutter on said bearing support by means of a spread piece in the axial gap between said trunnion and the component, inserted into and fixed to said roller cutter on the side of the trunnion base; an end bearing; and wherein said radial-thrust roller bearing, locking said roller cutter on said trunnion, is executed in the form of a separate internal ring and a separate external ring with bearing races, and rolling bodies corresponding to them.
 10. The bearing assembly as set forth in claim 9, wherein said radial-thrust roller bearing, locking the roller cutter on the trunnion, executed in the form of a separate internal ring and a separate external ring with bearing races, and rolling bodies corresponding to them, is provided with a cage.
 11. The bearing assembly as set forth in claim 9, wherein said end bearing is executed in the form of a separate internal ring and a separate external ring with bearing races, and cylindrical rollers between them.
 12. The bearing assembly as set forth in claim 9, wherein said end bearing is executed in the form of a radial-thrust conical roller bearing, comprising a separate internal ring and a separate external ring with bearing races, and rolling bodies corresponding to them, united by a cage, the internal ring of the said end bearing being fitted on the trunnion with a possibility of free movement along the trunnion, and with an axial rest of the said ring against the trunnion through a spring, e.g. a disk-type spring.
 13. The bearing assembly as set forth in claim 9 further comprising a thrust bearing between said roller cutter and said trunnion, executed in the form of a pair of supporting rings, with a cage having rolling bodies located between them, moreover, the said bearing resting against said trunnion end through a spring, e.g. a disk-type spring.
 14. The bearing assembly as set forth in claim 9, wherein said bearing, nearest to the trunnion base, is located inside the above component, inserted into and fixed to the roller cutter on the side of the trunnion base, the said component being screwed into the roller cutter on the side of the trunnion base to a rest of the radial-thrust bearing against the trunnion.
 15. The bearing assembly as set forth in claim 9, wherein said component, inserted into and fixed to the roller cutter on the side of the trunnion base, is executed in the form of a split spring ring. 